With less than 1% of production I consider the K-code a special order in itself. Do you happen to have a more accurate figure?
There are a couple of factors not included:
Marketing forecasts determined what model cars should be built well before actual production began to fill dealer inventory. That means that the first cars off the assembly line, "K" cars included, were not "special orders".
Is a "special order" from a dealer a "special order" or is it to fill inventory. My San Jose 65 GT Fastback was delivered to a Sacramento dealer, but was sold in a Redwood City dealership 3 months later. An inventory car.
A special order from a customer is just that, a "special order". It does not necessarily have an order number in the DSO.
Back to the original Query. In talking about the mis-matched VINs with a friend (between us, we own 5 HP Mustangs), there is another possibility, the original engine failed at final test. There was another engine available, so to make the earlier sale, it was swapped (we'll get another engine later). I have seen and documented a similar VIN problem where a 64 1/2 "D" code convertible was re-identified as a "F" code (5F08D192898 to 5F08F205641). The only conclusion was the engine failed. As it was real near the end of the production year, a decision was made to get it out of here and sell the car with whatever was available. The door data plate info - 76A M 86 20G 52 1 6. The last I saw the car was at a swap meet up for sale in California.
Jim